JPH066888B2 - Engine decompression device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine decompression device capable of reducing an operating force when starting an engine and preventing danger due to reverse rotation.

[Prior Art] Conventionally, there is known a decompression device that slightly opens an intake valve or an exhaust valve at the time of starting an engine to bring a combustion chamber into a half-compression state (decompression state) to reduce a starting load. This decompression device has a structure in which the combustion chamber is brought into a semi-compressed state manually or automatically. In the case of the manual type, the rocker arm is set to the decompression position by manually operating the decompression shaft provided on the cylinder head or the rocker shaft, and then the engine is started by the activation handle or the recoil starter. . On the other hand, in the case of the automatic type, for example, JP-A-50-9
Japanese Patent No. 5630 proposes a conventional technique relating to a compression pressure reducing device at the time of starting an engine using centrifugal force.

[Problems to be Solved by the Invention] However, unlike a gasoline engine, a diesel engine is designed to be started by injecting fuel into compressed air and spontaneously igniting the engine. The compression ratio is high, and the engine is manually operated. In order to rotate, a considerable auxiliary device (in addition to automatic decompression, auxiliary fuel injection hole, delay of injection timing, increase of flywheel mass, etc.) was required. That is, since the decompression lift position of a general gasoline engine is the cam crest decompression fixed to the cam crest, the decompression / lift position is 8th in relation to the compression ratio during operation.
As shown in the cam lift with respect to the crank angle in the figure, the position is limited to a position close to the bottom dead center in the early stage of the compression stroke. Therefore, there is a problem that the compression section becomes long, and particularly in a diesel engine, the operating force at the time of starting becomes large.

Further, as a result of performing various starting tests on the centrifugal decompression device of the diesel engine, the present inventors found that decompression is released in a certain rotation speed (cranking rotation speed) range as shown in FIGS. 9 and 10. , And found that a reversal phenomenon (so-called Ketchin phenomenon) occurs. This reverse rotation phenomenon occurs when air and fuel are mixed in the cylinder when the engine is started, and a torque opposite to the rotation direction of the engine is generated.
This is a phenomenon that causes reverse rotation. FIG. 9 shows a region where reverse rotation occurs with respect to the engine temperature, and the shaded portion B is the region where reverse rotation occurs. This region of reverse rotation occurs even in the low speed region as the engine temperature increases. The first
FIG. 0 shows the cranking rotation speed at the time of starting at the engine temperature C in FIG. 9, and the hatched portion D is the reverse rotation occurrence region.
In this figure, the curve E shows the case where the cranking speed is too low and the engine does not start because it has not reached the ignition temperature of the fuel, and the curve F shows that the cranking speed is in the reverse rotation occurrence region, and the curve F shows the reverse rotation. A case where a phenomenon occurs is shown, and a curve G shows a case where the engine starts at an appropriate cranking speed. In this figure, H is a range showing the decompression state, I is a range showing the decompression released and compressed state, and J is a range showing the engine ignition and starting state. In this way, a reversal phenomenon occurs in a certain number of rotation speeds, which may result in injury to the arm when starting the crank handle, or when the rope is started, the rope is caught or the arm is pulled back. There was a problem that such things occur. In addition, there is a similar problem in a gasoline engine having a large exhaust capacity.

The present invention has been made by paying attention to such conventional problems and the like, and does not require a troublesome preparation work before starting the engine, and can reduce the operating force at the time of starting the engine, and also the danger due to the reverse rotation. An object is to provide an engine decompression device that can be prevented.

[Means for Solving the Problems] In order to achieve the above object, according to the present invention, a centrifugal force of a flyweight caused by rotation of a cam shaft causes a decompression pin to project and retract from a cam surface, and the decompression state is caused by the projection to release decompression. In the centrifugal decompression device, the rotation speed range for releasing the decompression state is set to at least a rotation speed range higher than the reverse rotation generation region of the engine, and the decompression state section due to the protrusion of the decompression pin is set to the compression stroke. It was set to a partial area before top dead center, and was set so that the compression ratio before the start and the compression ratio after the end of this section in the decompression state were equal.

[Operation] With the above configuration, the rotational speed range for decompression cancellation is set to a rotational speed range higher than at least the reverse rotation generation range of the engine. Therefore, in that rotational range, the compression energy is accumulated by the rotational energy stored in the flywheel or the like. Since it will survive the (top dead center), the inversion phenomenon (Ketchin phenomenon) will not occur. In addition, the section where the decompression state of the decompression pin is set to a part of the compression stroke, and the compression ratio before the start of the section where this decompression state is set and the compression ratio after the end are set to be equal. The operating force at the time of starting can be reduced evenly.

Embodiments Embodiments according to the present invention will be specifically described below with reference to the drawings.

1 to 7 relate to an embodiment of the present invention, and FIG. 1 is a sectional view of a camshaft portion of a diesel engine, and FIG.
1 is a right side view of FIG. 1, FIG. 3 is a perspective view of a decompression pin, FIG. 4 is a view showing a cam lift with respect to a crank angle, FIG. 5 is an explanatory view showing a piston position and a combustion chamber volume,
6 and 7 are cross-sectional views taken along the line AA of FIG. 1, FIG. 6 is an operation explanatory diagram when the engine is started, and FIG. 7 is an operation explanatory diagram when the engine is normally rotating.

In these drawings, reference numeral 1 is a cam shaft, and cams 4 and 5 are formed on the cam shaft 1 so as to correspond to the ends of the intake valve tappet 2 and the exhaust valve tappet 3. Further, the camshaft 1 is provided with a cam gear 6 which is close to the cam 4 and receives the rotational force of a crankshaft (not shown). Anti-cam 4 of this cam gear 6
A groove portion 7 formed in a concave shape is provided on the side end surface.
A pin hole 8 parallel to the axis of the cam shaft 1 is formed on the end surface of the cam gear 6 corresponding to the groove portion 7. As shown in FIG. 2, the pin hole is provided at a position deviated from the compression top dead center position K in the cam gear 6 toward the compression bottom dead center position side (the rotation direction side of the cam gear 6 in the drawing) by an angle θ. Has been. A decompression pin 9 is inserted into the pin hole 8 and is rotatable in a predetermined angle range. The decompression pin 9 is formed in a shaft shape, and has an engaging portion 11 formed in a substantially U shape on one side of a shaft portion 10. The engaging portion 11 is located on the groove portion 7 side of the cam gear 6. It is rotatably provided. Further, the decompression pin 9 has an end portion on the side opposite to the engaging portion 11 extending toward the cam 4 side, and a semicircular notch 12 cut out at the end portion of the decompression pin 9 facing the end portion of the tappet 2. Is formed. The portion of the decompression pin 9 facing the end of the tappet 2 is projected and retracted from the outer peripheral surface of the cam 4 by the cam action of the notch 12 caused by the rotation of the decompression pin 9. On the other hand, a weight lever 13 is provided on the end surface side of the cam gear 6 in which the groove portion 7 is formed. One end of the weight lever 13 is rotatably attached to a pin 14 projecting from the end face of the cam gear 6 in a direction substantially perpendicular to the rotation center of the decompression pin 9 with respect to the axis of the cam shaft 1. The other end side is extended to the decompression pin 9 side so as to slightly go around the outer circumference of the camshaft 1. An engaging pin 15 is provided on the other end side of the weight lever 13 that extends, and the engaging pin 15 is engaged with the engaging portion 11 of the decompression pin 9. That is, the decompression pin 9 and the weight lever 13
And are designed to rotate in conjunction with each other. A return coil spring 16 having one end fixed to the cam gear 6 and the other end fixed to the weight lever 13 is fitted to the pin 14 projecting from the end face of the cam gear 6. The side provided with the engagement pin 15 is urged toward the axial center side of the camshaft 1. And the weight lever 1
3 mass and shape and return coil spring 16
The urging force of the engine avoids the cranking speed range where the engine reverse phenomenon (Ketchin phenomenon) occurs, and releases the decompression above that range. This reverse rotation generation area has a different numerical value depending on individual engine characteristics, and is determined empirically or experimentally. Further, the shape of the decompression lift due to the notch 12 of the decompression pin 9 becomes maximum at a position deviated from the compression top dead center position toward the compression bottom dead center position by an angle 2θ with respect to the crank angle, as shown in FIG. The decompression section K is formed in a mountain shape that gradually decreases on both sides. A first compression section L and a second compression section M are formed on both sides of this chevron. The first and second
If the compression ratios in the compression sections L and M are E ₁ and E ₂ , respectively, Becomes Here, as shown in FIG. 5, Vn ₁ is added from the valve closed position to the decompression start position, and Vc ₁ is added with the stroke volume from the decompression start position to the compression top dead center position and the combustion volume at the top dead center position. Vn ₂ is the volume of the combustion chamber from the decompression end position to the compression top dead center position, and Vc ₂ is the combustion chamber volume at the compression top dead center position. The value of θ is set so that E ₁ = E ₂ . The decompression pin 9 is provided on the shaft portion side of the cam gear 6 in which the groove portion 7 is provided.
A notch 17 is formed so that the can be rotated.

Reference numerals 18 and 19 in the figure denote push rods.

In such a configuration, first, when the engine is started, the urging force of the return coil spring 16 is larger than the centrifugal force,
The weight lever 13 and the decompression pin 9 are maintained counterclockwise as shown in FIG. The end of the decompression pin 9 provided with the cutout 12 projects from the outer peripheral surface of the cam 4 and pushes up the tappet 2 slightly to bring a combustion chamber (not shown) into a semi-compressed state. At this time, the decompression pin 9 is provided so as to be in a decompression state in a partial region of the compression process, and is divided into the first and second compression sections L and M to reduce the compression ratios E ₁ and E ₂ . In addition, since the respective compression ratios are made equal and the work amount is made the same, the operating force can be uniformly reduced.

Next, when the cranking rotation speed of the camshaft 1 becomes equal to or higher than the reverse rotation occurrence range of the engine, the weight lever 13 starts rotating clockwise as shown in FIG. 7, and the decompression pin 9 rotates together with it. Then, the decompression pin 9 is retracted from the outer peripheral surface of the cam 4 to release the push-up of the tappet 2, and as a result, the combustion chamber (not shown) is fully compressed.
At this time, since the decompression is released and the ignition is performed when the cranking rotation speed is equal to or higher than the reverse rotation occurrence region, the danger due to the reverse rotation phenomenon (Ketchin phenomenon) can be prevented.

With the above operation, the starting load can be reduced without requiring any troublesome preparation work before starting the engine. or,
In this embodiment, since the decompression pin 9 can be largely rotated by a slight rotation of the weight lever 13 due to the centrifugal force, the semi-compressed state can be released early in the diesel engine having a low rotation speed at the time of starting.

In the above embodiment, the case of large engine of, inflating the air compressed from Vn 2 ₊ Vc ₂ after decompression release until the volume of Vc _2, after the top dead center, to the bottom dead center in the explosion stroke Considering that the negative work is felt as a pulling force on the arm, the value of θ is set at the position where the work in the first compression section is equal to the sum of the work in the second compression section and the work in the expansion stroke. It may be set. Further, in the above-described embodiment, the U-shaped engaging portion 11 of the decompression pin 9 has the engaging pin 15 provided on the weight lever 13.
Is engaged and interlocked with each other, but it suffices that the decompression pin can be largely rotated by the weight lever 13. Furthermore, the shape of the decompression pin can be arbitrary according to the required decompression lift.

The present invention is not limited to the structure of the embodiment as long as it is a decompression device that operates the decompression pin by centrifugal force.
Further, the valve train that is slightly pushed up by the decompression pin to open may be either an intake system or an exhaust system. Further, the return coil spring 16 may be omitted. Furthermore, although a diesel engine is used in the embodiment, it can be similarly applied to a gasoline engine having a large exhaust capacity.

[Effects of the Invention] As described above, according to the present invention, in the centrifugal decompression device by the depressing action of the decompression pin, the rotation speed range for releasing the decompression state is set to a rotation speed range higher than the engine reverse rotation occurrence range. However, the decompression section is set to a part of the compression stroke, so no complicated preparatory work is required before starting the engine, and the operating force when starting the engine can be reduced and the risk of reverse rotation can be prevented. There is an effect that can be done.

Further, since the compression ratio before the start of the decompression section and the compression ratio after the end of the section are set to be equal, the operating force at the time of starting the engine is uniformly reduced, and good starting operability can be obtained. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 to FIG. 7 relate to an embodiment of the present invention, and FIG. 1 is a sectional view of a camshaft portion of a diesel engine, and FIG.
1 is a right side view of FIG. 1, FIG. 3 is a perspective view of a decompression pin, FIG. 4 is a view showing a cam lift with respect to a crank angle, FIG. 5 is an explanatory view showing a piston position and a combustion chamber volume,
6 and 7 are sectional views taken along the line AA of FIG. 1, FIG. 6 is an operation explanatory view at the time of engine starting, FIG. 7 is an operation explanatory view at the time of normal rotation of the engine, and FIG. FIG. 9 is a diagram showing the cam lift with respect to the crank angle of the engine according to the example, FIG. 9 is a diagram showing the occurrence region of the reverse rotation phenomenon with respect to the engine temperature, and FIG. It is a figure which shows a number. DESCRIPTION OF SYMBOLS 1 ... Cam shaft, 2, 3 ... Tappet 4, 5 ... Cam, 6 ... Cam gear 8 ... Pin hole, 9 ... Decompression pin 11 ... Engagement part, 12 ... Notch part 13 ... Weight lever, E1, E2 ... Compression ratio K ... Decompression state section L ... Section before decompression start M ... Section after decompression end

Claims (1)

[Claims] 1. A centrifugal decompression device in which a decompression pin is projected and retracted from a cam surface by centrifugal force of a flyweight caused by rotation of a camshaft, and the decompression state is released by the projection to release the decompression state. The rotation speed range is set to at least a rotation speed range higher than the engine reverse rotation generation range, and the section in the decompression state due to the protrusion of the decompression pin is set to a partial area before the top dead center of the compression stroke. An engine decompression device, characterized in that the compression ratio before the start of the section in the state and the compression ratio after the end are set to be equal.